Method and apparatus for the production of a work piece of exact geometry

ABSTRACT

This invention relates to a device and procedure for the production of a work piece with exact geometry and high surface quality, a form tool in particular. Preferably, the work piece is constructed using a process wherein powder coatings are applied one on top of each other, by means of compaction, said process being computer-controlled. After the powder has been compacted, the surfaces thereof are finely machined in a mechanical manner. During the entire machining process, the work piece to be produced is surrounded with powdery source material.

[0001] The invention relates to a method for the production of a workpiece by the successive compacting, by means of electromagneticradiation or particle radiation, of powdered starting material that hasbeen applied horizontally in layers, so that each layer consisting of atleast one trace comprises two substantially vertical lateral faces andone substantially horizontal upper face which, in turn, forms the basisfor a possible following layer, wherein at least one of the two verticalside walls is subject to mechanical finishing subsequent to thecompacting of the powdered starting material that has been appliedhorizontally in layers, and wherein the work piece to be formed issurrounded by powdered starting material during its production.Furthermore, the invention is directed to a device for performing theabove-described method.

[0002] DE 195 33 960 C2 discloses a method wherein one material layereach is applied on a base in the form of a trace and is subsequentlyfused or compacted, respectively, by means of a laser beam.Subsequently, a second layer is applied and compacted, and so on, withthe number of the layers applied and compacted by means of a laser beamdepending on the desired height of the work piece. On applying a newlayer, this new layer always combines with the surface of the layerapplied before. The powder-metallurgical production of the work piece isfollowed by a finishing of both the lateral faces and the surface bymeans of a cutting process. In the case of the known method it is takencare that non-melted powder is always removed from the working area byblowing or sucking it off.

[0003] With the method known, comparatively short production times canbe achieved for exactly dimensioned work pieces when the radiationdevice and the mechanical processing device are computer-controlled. Aproblem of the production method known, however, consists in that in theedge area of the work pieces produced, i.e. in the area of the lateralfaces, a non-uniform material consistency is generated and thatespecially porosities may occur.

[0004] For solution of this problem, DE 195 33 960 C2 suggests to fusematerial beyond the desired contour dimension and to remove thedistinctly projecting edges of the work piece by means of subsequentmechanical processing. By means of this procedure, it is indeed possibleto remove so much material in the area of the lateral faces that ahomogeneous material consistency can be achieved; this, however, rendersthe expenses, i.e. the working time and the tool costs, to becomeundesirably high.

[0005] It is therefore an object of the present invention to provide amethod which substantially reduces the materials expenses with amechanical finishing of the surface of the outer contour of the workpiece and simultaneously ensures a high surface quality of the outercontour.

[0006] In accordance with the invention, this object is solved by amethod for the production of a work piece by the successive compacting,by means of electromagnetic radiation or particle radiation, of powderedstarting material that has been applied horizontally in layers, so thateach layer consisting of at least one trace comprises two substantiallyvertical lateral faces and one substantially horizontal upper facewhich, in turn, forms the basis for a possible following layer, whereinat least one of the two vertical side walls is subject to mechanicalfinishing subsequent to the compacting of the powdered starting materialthat has been applied horizontally in layers, and wherein the work pieceto be formed is surrounded by powdered starting material during itsentire production, wherein the mechanical finishing of a vertical sidewall of an n^(th) layer is only performed after the generation of ann+x^(th) layer.

[0007] In the following, the respectively current layer, i.e. the layerthat forms the upper final layer at a particular point in time, isreferred to as n^(th) layer. All the layers positioned below this n^(th)layer are referred to as n−x^(th) layers, and all the layers that will,viewed from this point in time, still have to be produced in the future,are referred to as n+x^(th) layers.

[0008] In a preferred method of the present invention, the finishing ofthe n^(th) layer is started only when the geometric distance from then^(th) layer to an n+x^(th) layer positioned thereabove is so large thatno thermal impact having the effect of a distortion affects the n^(th)layer.

[0009] When producing a work piece in accordance with the methodaccording to the invention, the powdered starting material is applied inlayer-thickness on a base over an area which exceeds the contour of thework piece. In a next step, compacting of this powdered startingmaterial is effected in traces, with the trace width corresponding tothe sphere of action of the radiation. For the construction of a layer,which regularly consists of a plurality of traces, at least, however, ofmerely one trace, these traces are compacted such that the edge area ofeach individual trace overlaps the edge area of an adjacent trace suchthat a homogeneous trace is produced during the compacting of theadjacent traces. When producing a layer formed by traces, variousstrategies of tracing can be chosen.

[0010] For instance, the outermost contour trace is formed by a firsttrace, and subsequently the inner space formed within this closedcontour trace is filled by a meander-shaped pattern, so that ahomogeneous layer is finally produced. It is, however, also possible tofill the inner space that has been formed such by, for instance, aquasi-spiral pattern.

[0011] By the exact controlling of the compacting beam (electromagneticbeam or particle beam) it is further possible to adjust the materialcharacteristics in the area of the edge contour, i.e. the outermostcontour trace of the work piece.

[0012] With increasing beam power or energy supplied per area unit, theproportion of molten phase of the material increases, which results in ahigh compacting of the material and thus in good mechanical properties.In the direct edge area of the work piece, i.e. in the area of thelateral surface, such compacting of the powdered material will, however,also lead to an inexactness of the structure. A disadvantage of a highbeam intensity is the thermal effect which may lead to a subsequentpowder adherence in the n−1^(st) or in further layers. By therespectively repeated thermal impact of the n−x^(th) layers alreadyformed, a so-called distortion of the contour of the work piece mayoccur.

[0013] The method according to the invention takes this thermalinfluence of the work piece contour into account by performing themechanical finishing after the completion of a certain number of layersonly. In accordance with the invention, the finishing is only performedwith layers which are, by their distance to the currently producedlayer, not subject to a thermal impact effecting a distortion of thework piece.

[0014] In accordance with the invention, several layers can be finishedsimultaneously. If only individual layers are referred to in thefollowing description, these shall comprise also layer packages that mayconsist of a plurality of individual layers.

[0015] A decision on the number of the layers to be finished may, forinstance, depend on the contour shape. In the case of contours withfrequent changes of gradient, the finishing of few layers may be moreadvantageous than the finishing of several layers.

[0016] The method and the apparatus according to the invention will beexplained by way of example in the enclosed drawing. There shows:

[0017]FIG. 1 a schematic representation of an arrangement for performingthe method according to the invention.

[0018] In FIGS. 2 to 9, individual steps of the method according to theinvention are illustrated, wherein layer packages are shown for betterillustration of the method according to the invention. There shows:

[0019]FIG. 2 a schematic sectional representation of a work piece afterthe production of a first layer package;

[0020]FIG. 3 a schematic sectional representation of the work pieceaccording to FIG. 2 with a second layer package;

[0021]FIG. 4 a schematic sectional representation of the work pieceaccording to FIG. 3, with the first layer package being finished;

[0022]FIG. 5 a schematic sectional representation of the work pieceaccording to FIG. 4, after the generation of a further layer package;

[0023]FIG. 6 a schematic sectional representation of the work pieceaccording to FIG. 5, after completion of the finishing of a furtherlayer package;

[0024]FIG. 7 a schematic sectional representation of the work pieceaccording to FIG. 6, after the generation of a last layer package;

[0025]FIG. 8 a schematic sectional representation of the work pieceaccording to FIG. 7, after completion of the finishing of thepenultimate layer package;

[0026]FIG. 9 a schematic sectional representation of the work pieceaccording to FIG. 8, after completion of the finishing of the last layerpackage.

[0027] In the arrangement according to FIG. 1, the work piece to beproduced is denoted with 1. The production is effected such thatpowdered starting material 3 at an exactly predetermined layer thicknesss is applied on a working table 5 that may be moved up and downvertically by means of a lifting device 7 in arrow direction 27. Thestarting layer thickness equals to the layer thickness of layer n, layern−1 or layer n−2 illustrated in the drawing. The area of the powderedstarting material applied has to exceed the desired final contour of thework piece.

[0028] Above the working table 5, a processing unit 20 is arranged whichcan be moved in its entirety in arrow direction 29 as well as preferablyperpendicularly to the drawing plane. The movement of the processingunit 20 is computer-controlled by a control device 11 which alsosimultaneously controls the lifting movement of the working table 5. Theprocessing unit 20 substantially comprises a radiation source 6, one orseveral mirrors actuated by an actuating unit 10, or a comparableguiding device for the beam 18 emanating from the radiation source 6 soas to guide it by means of two-coordinate control on the working table 5in correspondence with the desired component contour. In addition to theradiation device 6, 8, 10 the processing unit 20 also comprises aprocessing device for mechanical finishing. The processing deviceillustrated in FIG. 1 is a milling tool 2 with an appropriate drive unit9 which is also controlled by the control unit 11. As is illustrated inFIG. 1, the milling tool 2 immerses into the powdered starting material3 for mechanical finishing, so that the work piece 1 is surrounded bypowdered finishing material 3 during its entire production and thus alsoduring the entire mechanical finishing. Furthermore, a dressing bar 4 isprovided at the processing unit 20, by means of which powdered startingmaterial 3 that was applied on the working table 5 can be distributed atconstant layer-thickness by transverse movement of the processing unit20 relative to the working table 5. The dressing bar 4 maysimultaneously be designed as a feeding device for the powdered startingmaterial 3.

[0029] After applying the first layer of the powdered starting material3 on the working table 5, the starting material is compacted in adesired trace by a corresponding control of the beam 18 and, asrequired, additionally by the relative movement of the processing unit20 to the working table 5. Each time after one layer has been appliedand compacted, the working table 5 is lowered by one layer-thickness bymeans of the lifting device 7.

[0030] Following the radiation and compacting of the powdered startingmaterial to form a first (n^(th) layer), further (n+1^(st); n+2^(nd);n+3^(rd); . . . ; n+x^(th)) layers are applied and compacted by thismethod corresponding to a desired contour which is preferably stored ona record. Only after the generation of a current layer which is spacedapart from a non-finished layer to such an extent that the thermaleffect emanating from this current layer does not or is not able toeffect any distortion with this non-finished layer is the mechanicalfinishing of this non-finished layer started.

[0031] Once this criterion of the thermal non-influencing of the n^(th)layer has been fulfilled with regard to the n−x^(th) layer, thefinishing of the n−x^(th) layer is started. As has been mentionedinitially, the same is applicable to the n^(th) layer package withregard to the finishing of the n−x^(th) layer package.

[0032] The arrangement according to FIG. 2 illustrates a work piece 1after the production of a first layer package A having the height Δz,illustrated in double hatching density. The work piece 1 is mounted on abase S, with the height of the base S advantageously corresponding tothe milling offset Δh. The work piece 1 is to obtain a final contourthat corresponds to the contour 2 and lies within a contour body 3. Thiscontour body 3 is produced from a particular number of layer packages ofthe height Δz, which in turn consist of a plurality of layers. Thedimensional difference between the contour body 3 and the work piece 1is removed by the mechanical finishing, so that the completed work piece1 is available after the mechanical finishing of the last layer package.

[0033]FIG. 3 illustrates the condition of the work piece 1 after thegeneration of the second layer package B above the first layer packageA, with the second layer package B also having a height of Δz. It is,however, also possible to vary the height of each layer package, forinstance as a function of the contour shape of the final contour. In thecase of contours with substantial change of gradient of the surface, alower layer package height might also be of advantage. Likewise, thelayer package height may depend on the type of miller. Basically, thelayer package height will have to he chosen such that any desiredcontour may be achieved with the selected miller by keeping to thedesired surface quality. A substantial technical dimension may, forinstance, be the radius of a ball nose end mill.

[0034]FIG. 4 illustrates the condition after the completion of the firstmechanical finishing of layer package A. The mechanical finishing ispreferably performed by means of an end mill or a ball nose end millwhich removes the dimensional difference between the contour body 3 andthe final contour 2 of the work piece 1. After completion of thefinishing, a new layer package is produced, wherein the finishing isalso postponed until at least the next layer package has been produced.

[0035]FIG. 5 schematically illustrates the condition of the two layerpackages M and M+1. FIG. 6 illustrates the finished layer package M. Asis illustrated in FIG. 7, the last layer package M+2 which is positionedabove the layer package M+1 is advantageously dimensioned such that itprojects by a certain amount H-h over the actual final contour height h.With the completion of the last layer of the layer package M+2, thelayer construction of the work piece 1 has been completed.

[0036] In the following working step, illustrated in FIG. 8, themechanical finishing of the layer package M+1 is performed, wherein,caused by the contour shape, portions of the projecting layer packageM+2 can also be removed already. The projecting remainder of the layerpackage M+2 that has now been left is, as illustrated in FIG. 9, removedby means of the last mechanical finishing. With this last working step,the production of the work piece 1 is totally completed.

1. A method for the production of a work piece by the successivecompacting, by means of electromagnetic radiation or particle radiation,of powdered starting material (3) that has been applied horizontally inlayers, so that each layer consisting of at least one trace comprisestwo substantially vertical lateral faces and one substantiallyhorizontal upper face which, in turn, forms the basis for a possiblesubsequent layer, wherein at least one of the two vertical side Walls issubject to mechanical finishing subsequent to the compacting of saidpowdered starting material (3) that has been applied horizontally inlayers, and wherein the work piece (1) to be formed is surrounded bypowdered starting material (3) during its production, wherein themechanical finishing of a vertical side wall of an n^(th) layer isperformed after the generation of an n+x^(th) layer only.
 2. The methodaccording to claim 1, wherein at least one further layer has beenproduced between the production of the n^(th) layer and the beginning ofthe mechanical finishing of this layer.
 3. The method according toclaims 1 or 2, wherein several layers are finished simultaneously. 4.The method according to claim 1, wherein several layers are comprised toform layer packages.
 5. The method according to claim 4, wherein themechanical finishing of the n−1^(st) layer package is started after thegeneration of an n^(th) layer package.
 6. An apparatus for theproduction of a work piece, in particular by performing a methodaccording to any of claims 1 to 5, consisting of a working table (5) tobe lowered which can be covered by a powdered starting material (3), aprocessing unit (20) that is designed to be vertically and horizontallymoveable and can be connected to act with a control device (11), whereinsaid processing unit (20) comprises at least one radiation source (6)and at least one mirror unit (8) controllable by an actuating unit (10),so that a beam (18) emanating from said radiation source (6) is guidableon the working table (5) via the at least one mirror unit (8) that iscontrollable by means of a two-coordinate control in correspondence witha desired component contour, wherein said processing unit furthercomprises a processing device for the mechanical finishing ofsubstantially vertical faces, and wherein the control device (11)further comprises means for controlling the mechanical finishing of ann^(th) layer with time delay vis-a-vis the completion of an n+x^(th)layer, depending on the thermal characteristics of the work piece to beproduced.